Smoke rises over Bangkok where worsening political unrest has prompted the Foreign Office to issue a travel warning. Photograph: Manan Vatsyayana/AFP/Getty Images

The Foreign Office today warned Britons against travelling to Bangkok, where its embassy remained closed owing to worsening political unrest in Thailand.

"If you are already in Thailand, we advise against all but essential travel to the city of Bangkok," it said on its website. "Wherever possible, you should take transport services which do not involve transiting areas of Bangkok where political protests are taking place."

The FCO described the situation in the Thai capital as highly unpredictable, adding: "British nationals in Bangkok should stay indoors and monitor this travel advice and local media."

It explained that it had had to close the British embassy because of unrest in the Ratchaprasong area, but was still offering consular services elsewhere in the capital.

Travellers were also informed that there had been reports of violence in the north-eastern cities of Khon Kaen and Udon Thani, and of protests and gunfire in the northern city of Chiang Mai.

But the FCO pointed out that Bangkok's Suvarnabhumi airport was operating, adding that the travel warning did not apply to passengers passing through the airport on their way to other destinations.

It also reminded visitors of the curfew imposed last night and advised them to make sure they kept their documents on them."You should carry your passport or some form of ID and evidence of residence to gain access if stopped by the authorities."

This afternoon, the Thai government announced that a curfew relaxation would be extended to those carrying passports and travel documents, allowing foreign tourists and Thai travellers to go to Bangkok airports.